For preparing a processed cereal product, such as polished rice, polished wheat or polished buckwheat, there have practically been used a grinding machine, rice-polishing machine, de-coating machine and the like for removing a superficial layer including seed-coat or pericarp from raw grain, such as brown rice, raw wheat or raw buckwheat. The fundamental mechanism therefor resides in a dynamic action by the impingement or abrasion of cereal grains against each other or impact upon the hitting of grains by a mixer blade or beater onto a hard surface, such as a hard rubber plate, in order to remove a surface layer of such grains. However, such conventional techniques by means of impact cannot realize the removal of a surface coat layer at fine concavities including secluded or recessed portions or thin wrinkles, such as seed surface grooves of wheat, seed surface canals of barley and so on, though valuable portions, such as germs and other parts, may be cut off. While there has been practiced a rice polishing technique in which unpolished rice grains are pressedly guided by, for example, a screw or the like, through a guide path inside an outer cylinder provided with punched elements so as to realize the removal of a grain superficial layer by abrasion due to the frictional action between grains with each other and between the inside structure of the outer cylinder and the grains, this technique suffers from a disadvantage of being subject to heat evolution which may result in the denaturation of taste and decomposition of useful components.
Hulls or husks of grains, such as rice or the like, can be removed by passing the grain through a gap between rubber rolls in a husker, however, pericarps of buckwheat (buckwheat husks) can only difficultly be removed by a husker. For removing or abrading a superficial layer of grain of wheat or the like, there has been practiced a method in which the grain is passed through a gap between confronting abrading rolls. Also by this method, however, it is difficult to abrade off a grain surface layer within a recessed site, such as a seed groove of wheat or surface canal of barley. As explained above, it has been difficult to attain processing of a granular material, such as cereal grains, by conventional surface-treating methods without suffering from denaturation due to the debasement of the intrinsic properties of useful components by deactivation caused by heating and oxidation due to the heat evolution during processing operations, while attaining the removal of useless parts, such as useless superficial layers, surface grooves and so on.
In Patent Document 1 (JPA 10-15408), a rice polishing machine is disclosed, in which a rotary element provided on its outer circumferential face with brush means is rotated in a cylinder within a layer of rice stored in the cylinder to polish the rice. Here, the brush means functions only to move local rice grains around the brush means aside within the stored rice layer upon the rotation to effect mutual friction between the rice grains, so that the essential action of the brush means does not differ from that of conventional rotary blades or beaters and the attainment of the removal of a grain superficial layer at narrow secluded or recessed portions, such as grain seed grooves of wheat or seed surface canals of barley, is not possible.    Patent Document 1: JPA 10-15408